Arrangement for an instrument which comprises or is connected to a driving-in tool

ABSTRACT

An instrument is connected to a driving-in tool or drilling tool for elements on or in the form of an implant or drill for dentine. The tool includes an electric motor, the torque of which can be sensed, and which can be controlled by a control unit. A display unit is arranged so as to partly or fully display a curve representing the driving-in function performed. A tightening function is determined by a scale based on the slope of the curve, wherein a flatter slope represents a lower quality function and a steeper slope represents a higher quality function. A frictional resistance which exists for an element during the driving-in of the element can be determined in order to allow secure locking (preload) of the element by tension in the material of the element. A torque-time curve can be used assess the bone quality of bone being implanted or drilled.

TECHNICAL FIELD

The present invention relates to an arrangement for an instrument orsuch an instrument which comprises or is connected to a screwing-in ortightening tool, referred to here as a driving-in tool, for elements onor in the form of an implant or drill for bone, in particular dentine.In this connection, the tool comprises an electric motor which can becontrolled by a control unit. Also included is a unit which senses feedcurrent in the electric motor and, depending on the sensing, emits asignal depending on the torque of the electric motor, by means of whichsignal a torque or torque-angle curve can be represented. Also includedis a display unit which is arranged so as to display fully or partly adriving-in or tightening function performed. Thus the display unit candisplay, for example, curves or collected or individual values.

STATE OF THE ART

The present invention constitutes a development of inter alia theequipment indicated in PCT publication WO 98/27886, which relates to asurgical instrument to which a tightening tool according to the abovecan be connected and which instrument includes a display unit in orderto display inter alia a torque-angle value. The instrument is used interalia to screw implants or fixtures tight in the dentine. The instrumentcan also be used to screw down a screw tap in a hole made in thedentine. Furthermore, the instrument can be used to screw elements inthe form of screws tight in association with said implants and spacerelements belonging to these and other prosthetic constructions. Theknown instrument comprises a control unit for controlling the electricmotor and also sensing means which sense the current in the feed circuitof the motor and, depending on the sensing, supply information tomicroprocessor-based equipment.

The present invention is also based on what is previously known throughPCT publication WO 95/20146 which indicates equipment for inter aliascrew-driving and in which the structure in question must fit againstthe interacting structure with a high degree of accuracy. One of themain objects of this invention is that there are not to be any residualstresses or strains which are built into the structure as a result ofassembly.

DESCRIPTION OF THE INVENTION TECHNICAL PROBLEM

There is a requirement to be able to improve further the previouslyknown instruments. In this respect, it is desirable in practice, forexample, to be able to perform practical analysis aimed directly at thequality of the driving-home or tightening function in screw joints. Theinvention solves this problem inter alia.

It is also desirable to have a simple and readily understandableindication of the quality of the tightening function in question. Theinvention solves this problem also.

In connection with the driving-home of screws in implants or equivalent,the screwing-in function can be impaired by bone penetrating, forexample, between fixture and spacer. Another source of defects may bethat the spacer in question is not sufficiently well fitted or anchoredon the implant. A further factor which can distort the driving-homefunction is if the entire prosthetic function as such is poorly aligned.There is a requirement for sources of defects of said type not to becapable of impairing the driving-home result, but for it to be possibleto detect them at an early stage during the installation work. Theinvention solves this problem also.

There is a requirement to be able to determine and check a desired orpredetermined anchoring load in the element or screw concerned or thesecuring force in the screw connection. The invention solves thisproblem also.

There is in this respect a requirement to be able to identify thefrictional resistance the element or screw encounters in the screwing-infunction concerned. The invention solves this problem also.

There is also a requirement to be able to evaluate or assess the bonequality during ongoing implant preparation. According to previouslyknown instruments, the bone hardness can be evaluated during preparationin connection with threading of a prepared hole using a screw tap or aself-tapping fixture. The disadvantage of previously known methods isthat the surgeon has an opportunity to establish the bone quality onlyafter the hole has been drilled. It would be a great advantage if thesurgeon could know the bone hardness before making a decision on whichdrill diameter to use for the final preparation. The invention aims tosolve this problem inter alia.

There is also a requirement to be able to establish, during thedriving-in function, whether the implant is rotating without followingthe pitch of the implant in the axial direction, which means that thethreads are being destroyed in the bone. The invention aims to solvethis problem also.

SOLUTION

An arrangement of the type referred to in the introduction can beconsidered to be characterized mainly in that the sensing and/or displayunit determines the quality of the tightening function by means of ascale based on the slope of the torque-angle curve produced. Accordingto the invention, a flatter slope of the curve represents lower qualityand a steeper slope represents high quality.

The invention can also be considered to be characterized mainly in thata calculating unit, for example in the sensing and/or display unit, isarranged so as to determine, in the tightening function, a frictionalresistance which exists for the element during its driving-in orscrewing-home in order to make possible the application of an accuratedesired or predetermined loading which brings about secure locking(preload) of the element by means of tension or elasticity movement inthe material of the element.

In a development of the inventive idea, the element consists of a screwassociated with the implant/the fixture and the spacer. The display unitcan in this connection be arranged so as to display said scale, forexample a scale running between 1 and 10, where 10 indicates goodquality and 1 indicates poor or inferior quality. The slope can bedefined with a starting point from a base value of the torque. The slopecan also be defined from a base value up to the maximum torque value inquestion and also by means of the range of degrees of rotation for thesloping part concerned of the curve.

Said developments can also relate to a screw which is first intended tobe screwable home with frictional resistance inter alia via its screwthread and can then be anchored by means of tension or elasticity in thescrew material (preload) which is required for the anchoring loading onthe screw. Said calculating unit can operate with a torque value whichconstitutes part of a set torque value and brings about tightening ofthe element or screw. In this connection, a first measured value can beestablished. The calculating unit can also establish a second measuredvalue when the element or screw is subsequently loosened. Taking as itsstarting point said first and second value, the calculating unit canwork out a frictional resistance according to a formula indicated below.The calculating unit can then work out the torque value in question bymeans of adding to the frictional resistance worked out a value whichgives the desired or predetermined secure-locking loading (preload) onthe element.

An arrangement for evaluating the bone quality during implantpreparation can be considered to be characterized mainly in that thesensing unit senses torque generated by the electric motor duringdrilling in the bone, in particular dentine, of a hole for a screw tapor a threaded implant, and in that the display unit indicates, dependingon the sensing, a torque-time curve, by means of which the quality ofthe bone can be read off during drilling.

In developments of the inventive idea, the sensing unit senses thetorque during drilling and the calculating unit is then arranged so asto calculate power consumption per millimeter of drilled hole/implant.Empirical evaluations can also be included as a component in the qualityread-out. A curve displayed on the display unit indicates the averagepower per millimeter of implant. The drill speed can also be included inthe calculation.

The invention is further characterized in that the sensing unit sensestorque generated by the electric motor during tapping of the implantinto the bone, preferably the dentine, and in that a calculating unit,for example in the sensing or display unit, is arranged so as toestablish, during the driving-in function, whether the implant isrotating without following the pitch of the implant in the axialdirection, that is to say the threads are being destroyed in the bone,and also in that said arrangement warns the user that this is takingplace or stops the rotation of the implant.

ADVANTAGES

By means of the proposals made above, previously known instruments canbe supplemented with new functions which are of value in being able toperform the practical work. The possibility of integration into knowninstruments has economic advantages. Furthermore, it is possible toprevent stresses being built into the implant constructions withimplants, spacers etc. The torque-speed curve in question duringdrilling can give the user sufficient information for interpretinghis/her own actions because he/she knows his/her own drilling style andthe arrangement can therefore be an extremely valuable diagnostic tool.As the user also establishes more and more references in the actionshe/she takes, the accuracy of interpretation will increase.

LIST OF FIGURES

A for the present proposed embodiment of an arrangement which has thesignificant characteristics of the invention is described below withsimultaneous reference to the appended drawings, in which

FIG. 1 shows in the form of a basic diagram and from the front, asurgical instrument and, connected thereto, an electric motor with atool for acting on an element,

FIG. 2 shows in partial vertical section an example of a screw in apartly shown implant and spacer element,

FIG. 3 shows a torque-angle graph,

FIG. 3a shows a table defining quality values of tightening values,

FIG. 4 shows a torque graph,

FIG. 5 shows a functional diagram which can be implemented in acalculating unit or equipment used, and

FIG. 6 shows in screw form a torque-time curve for evaluating orassessing bone quality during implant preparation.

DETAILED EMBODIMENT

In FIG. 1, a surgical instrument is indicated by 1. The instrumentcomprises a display unit 2 which can consist of a data screen, a VDU,lamp arrangement etc. In the case of a screen, the instrument canrepresent torque-angle curves, all or parts of a screw-tighteningresult, the quality-determination function etc. The instrument comprisesin a manner known per se a power supply unit 3 and a unit 4 whichcontrols an electric motor 5 connected to the instrument. The connectionis in this respect made via a symbolically indicated connection 6, andtwo of the connecting conductors of the motor are indicated, namely 7and 8. The electric motor or the tool part 5 has in a manner known perse a unit 9 performing screw-tightening. The instrument also comprises aunit 10 which senses the feed current i1 of the electric motor, and alsoa calculating unit 11. The instrument is itself microcomputer-based andalso comprises memory functions in accordance with known correspondinginstruments. By means of the unit 10 and/or 11, a signal i2 depending onthe sensing is obtained.

FIG. 2 relates to a screw function on the implant, shown quitegenerally. A screw is indicated by 12 and parts of a spacer element oranother construction element are shown by 13. The element is arranged onan implant 14 which is partly shown. The implant is intended to bescrewable home in a premade hole 15 in dentine 16. The screw 12 isprovided with a thread 12 a which can be screwed into an internal thread13 a in the element 13.

The tool 5 to 9 can thus be applied to a screw slot 12 b on the screw.According to the idea of the invention, a practical analysis is to beperformed by the instrument with direct feedback on the quality in thetightening function in the screw connection 12, 13 via the threads 12 aand 13 a respectively. As the screw 12 a is tightened, a correspondingtorque-rotation curve according to FIG. 3 is obtained. FIG. 3 showsthree different curves 17, 18 and 19. The vertical axis of the graphshows the torque values, while the horizontal axis shows the degreevalue α. A base value B for the torque is indicated in the graph by adashed line parallel to the horizontal axis. Also indicated is a pointMT which indicates the maximum torque value in the case concerned. Thecurve 17 has a flat part 17 a which follows the base value B and also asloping part 17 b which slopes relatively steeply. Correspondingly, thecurve 18 has a part 18 a which essentially follows the base value B andmerges with a sloping part 18 b which has a gentler slope than the slope17 b of the curve 17. The curve 19 does not have a part following thebase value B but has a shape which essentially slopes throughout up tothe value MT at the outer degree value. The slope of the curve 19 isflatter than the slopes 17 b and 18 b of the curves 17 and 18. The slope17 b extends between degree values 30-55 roughly and a more accuratelyworked out degree value range is indicated by 22 in the diagram. Theslope 18 b extends from degree value 12 to 55 roughly and the degreevalue range is in this case indicated by 42. The curve slope of thecurve 19 extends over the majority of the degree value range indicated,which, for the curve 19, has been indicated as 55.

By means of the arrangement, a quality index can be obtained. The indexor the scale can extend between 1 and 10, where 10 means good qualityand 1 means poor quality. The quality of the tightening can be impairedby bone being present between the spacer and the implant (cf. thesurfaces 13 b and 14 a in FIG. 2). Other aggravating circumstances maybe that the spacer 13 is not satisfactorily fitted to the implant 14 orthat the entire installation arrangement of implant, spacer etc. ispoorly aligned. If one, two or all three of the above problems arepresent, the curves will be relatively flat, compare the curve parts 17b and 18 b and also the curve 19. According to the above, the index orthe quality is calculated from a degree value range from said base valueB up to the maximum torque MT.

The table according to FIG. 3 indicates the quality divided into a 10°scale. The maximum quality 10 exists if the curve slope begins at 45°and reaches the maximum value MT from the base value. The degree valuerange is in this case 10°, that is to say the Q value=10. The next stageis if the curve slope extends from roughly 35° to 55° and reaches themaximum value MT within this degree value range etc. On this calculationbasis, the curve 17 has a value of Q=9, the curve 18 a value of Q=7, andthe curve 19 a value of Q=5.

According to FIGS. 4 and 5, a method and arrangement for determining andcontrolling the anchoring force (preload) in a screw connection are madepossible. The torque required in order to tighten a screw connection canin principle be divided into two parts, namely on the one hand frictionand on the other hand the torque required to tension or bring aboutelasticity movement in the screw to a given anchoring load (preload).The problem with using existing torque-controlling methods fordetermining the anchoring load is that if the friction differs betweendifferent screw connections and the connection is to be controlled bychecking the torque applied, the anchoring loading (preload) willdiffer. If the screw 12 is tightened, the torque for this can be shownon the display unit 2. The torque will rise from close to 0 to a certainvalue, compare FIG. 4. The torque will then be equal tofriction+anchoring load. If the screw is loosened, the torque shown willbe equal to friction−anchoring load. If the screw is first tightened andsubsequently loosened again, it is possible to calculate or work out theanchoring value in question and thus the friction also. The screw canthen be tightened to its final torque value, which is worked out in sucha manner that the friction component is eliminated and that a veryaccurate anchoring load can then be applied in the screw connection,compare the screw 12 and the element 13 in FIG. 2. According to the newarrangement and method, the functional diagram according to FIG. 5 isfollowed. In a first stage 20, a torque is selected. The screw is thentightened to half torque, and a measured value T1 is read off accordingto 21. The screw is then loosened, after which a measured value T2 isrecorded according to box 22. Using the values thus measured, thecalculating unit (cf. 11 in FIG. 1) can work out a friction according tothe formula F=T2+(T1−T2)/2, cf. block 23 in FIG. 5. Tightening to thefinal torque value, which corresponds to a certain or predeterminedvalue for anchoring or tensioning, can then be carried out, compareblock 24. The above is also indicated in FIG. 4 where the vertical axisshows the torque T and the horizontal axis shows the rotary movement n.The values T1 and T2 are indicated on the vertical axis. A value T3 isalso shown, as are a range a which indicates the anchoring loading and arange b which indicates the friction. Two curves are shown by 25 and 26.

According to the present invention, a possibility is afforded forimproved assessment or evaluation of the bone quality during ongoingimplant preparation or drilling of holes in dentine. It is possible perse to measure the torque during drilling and also the speed of thedrill. These parameters will make it possible to represent the inputpower and, with knowledge of time and implant length, it is possible tocalculate in said calculating unit 11 (see FIG. 1) the average inputpower per millimeter of implant. In order to obtain an accurate pictureof the bone quality, the drilling depth would need to be included so asto obtain the power per millimeter of implant continuously for theentire implant length. However, the torque-implant rotation curve 27during drilling provides the user with sufficient information tointerpret his or her own actions because he/she knows his or her owndrilling style and the result can therefore be a useful diagnostic tool.

In FIG. 6, the vertical axis shows the torque in Ncm and the horizontalaxis shows time. An input value can in this connection be that theimplant length is 10 mm. The output value gives the average power W/mm.

It is also possible to see on the graph whether the implant, duringtapping, is rotating without going in. This would mean that the threadsare being destroyed in the bone. The arrangement can therefore beprovided with means which indicate such a case. The sensing unit sensestorque generated by the electric motor during tapping of the implantinto the bone, and a calculating unit, for example in the sensing ordisplay unit, is arranged so as to establish, in the driving-infunction, whether the implant is rotating without following the pitch ofthe implant in the axial direction. If this is the case, a warningsignal is given to the user or the rotation of the implant is stopped.

The invention is not limited to the embodiment shown above by way ofexample but can undergo modifications within the scope of the patentclaims below and the inventive idea.

What is claimed is:
 1. Arrangement for an instrument which comprises oris connected to a driving-in tool for an element on or in the form of animplant or drill for bone, in which the tool comprises an electric motorwhich can be controlled by a control unit, and in which a unit whichsenses feed current in the electric motor and, depending on sensing ofthe feed current, emits a signal depending on the torque of the electricmotor, which signal represents a torque curve or torque-angle curve, andin which a display unit is arranged so as to display fully or partly adriving-in function performed, according to one or more of the followingalternatives: a) at least one of the sensing and display unit determinesa quality of the tightening function by means of a scale based on aslope of said torque curve or said torque-angle curve, wherein a flatterslope represents lower quality of the tightening function and a steeperslope represents higher quality of the tightening function; b) acalculating unit in one of the sensing unit and the display unit isarranged so as to determine, in the driving-in function, a frictionalresistance which exists for the element, when the element is in the formof a screw, during driving-in of the element in order to make possiblethe application of a desired loading which brings about secure lockingby means of tension or elasticity movements in material of the element;c) the sensing unit senses torque generated by the electric motor duringdrilling in the bone of a hole for a screw tap or a threaded implant,and that the display unit indicates, depending on the sensing of thefeed current, a torque-time curve, wherein a quality of the bone can beread off during drilling based on the torque-time curve; d) the sensingunit senses torque generated by the electric motor during tapping of theimplant into the bone, and that a calculating unit in one of the sensingand the display unit, is arranged so as to establish, in the driving-infunction, whether the implant is rotating without following a pitch ofthe implant in an axial direction and threads are thereby beingdestroyed in the bone, in which case a warning signal is given to a useror rotation of the implant is stopped.
 2. Arrangement according to claim1, wherein the element consists of a screw associated with the implantand spacer, and wherein at least one of bone being present between theimplant and the spacer, the spacer having a poor connection to theimplant and the spacer and the implant having poor alignment contributesto imparting to the torque curve or the torque-angle curve a flatterslope compared with a case in which connection and alignment of theimplant and spacer are correct.
 3. Arrangement according to claim 1,wherein the display unit displays a scale running between 1 and 10,where 10 indicates good quality and 1 indicates poor quality. 4.Arrangement according to claim 1, wherein the slope is defined with astarting point from a base value of the torque.
 5. Arrangement accordingto claim 1, wherein the slope is defined from the base value up to themaximum torque value in question and also by the range of degrees ofrotation for the sloping part concerned of the curve.
 6. Arrangementaccording to claim 1, wherein the element consists of a screw which canfirst be screwed home with frictional resistance inter alia via itsscrew thread and can then be anchored by means of tension or elasticitymovement in the screw material which is required for anchoring loadingof the screw.
 7. Arrangement according to claim 1, wherein thecalculating unit operates with a torque value which constitutes part ofa set torque value and brings about tightening of the element or screw,and wherein, in this connection, a first measured value can beestablished.
 8. Arrangement according to claim 1, wherein thecalculating unit establishes a second measured value when the element orscrew is loosened.
 9. Arrangement according to claim 1, wherein thecalculating unit works out the frictional resistance according toF=T2+(T1−T2)/2.
 10. Arrangement according to claim 1, wherein thecalculating unit works out the torque value in question by means ofadding to the frictional resistance worked out or the force for thisforce which gives the desired or predetermined tightening loading(preload) on the element or screw.
 11. Arrangement according to claim 1,wherein the sensing unit senses the torque during drilling, and whereinthe calculating unit is arranged so as to determine power consumptionper millimeter of implant.
 12. Arrangement according to claim 1, whereinempirical evaluations are included in a read-out function for bonequality.
 13. Arrangement according to claim 1, wherein a curve displayedby means of the display unit indicates average power per millimeter ofimplant.
 14. Arrangement according to claim 1, wherein drill speed isalso included in calculations related to the driving-in function.